| Film cooling is an important means to protect the hot end components of aero-engine.Good film-cooling hole structure can reduce the consumption of cold air and guide the airflow to cover the surface better of the blade in order to improve the effect of film cooling.The smaller Length Diameter Ratio of film cooling hole is,the more severe influence of the hole structure on the flow of cooling air is.At present,internal cooling structure is more and more complex,leading the wall thickness of the film cooling hole is smaller and smaller.So,the influence of hole structure will be more severe which can not be ignored.This paper arranged the cooling mechanism of film holes,and focused on the influence of angle factors on film cooling.After studied the future direction of hole structure pattern,a new type of hole which could be easily processed was proposed: wave hole,and it could be divided into single wave hole and double wave hole according to the different position of branch hole.Combined cylindrical hole,B-shaped fan hole and NEKOMIMI hole,the two wave hole structures were simulated and horizontally comparative analysis.The longitudinal analysis of cooling mechanism in wave holes was analyzed comparing the different position of branch hole.Results show that the cooling efficiency of single wave hole is the same as that of double wave hole under low blowing ratio,which is the best among five hole types compared;the cooling efficiency of double wave hole under high blowing ratio is the best over all.Compared with fan-shaped hole in M=1.5,the cooling efficiency in centerline of double wave hole is increased by 58%,and the average cooling efficiency in spanwise is increased by 50%.Good cooling capacity of wave hole is lead by the contraction and expansion sections which were coupled the main hole and the branches at different positions.Cooling airflow through different positions would be affected by the pressure gradient and the reverse pressure gradient,which resulting in low exit velocity and reasonable velocity distribution.There will be three saddle points caused by the coupled structure which can greatly reduce the capacity of mixing in the reverse flow zones on both sides,causing the distance between two kidney vortex centers increased and the height of kidney vortex center decreased,it promote air film to adhere the wall surface and greatly increased the film cooling effect.Based on the comprehensive consideration of future requirements for cooling structure and processes in hole structure machining,single wave hole was selected for multi-parameter analysis.The angle parameters were choosed by the summary of research status and mainly discussed the influence on cooling efficiency of the wall surface when inclination angle α of the main hole,expansion angle β and backward angle γ of the branch hole changes.Within the parameter ranges researched,α =20° is the best inclination angle.As the inclination angle becomes larger,the Coanda effect would be more obviously,the velocity in outlet would be lower,and the coverage of gas film would be better.When M=1.5,the average cooling efficiency in surface of α =20° achieves 0.21,which is 3.5 times of the other hole types;β =20° is the best in expansion angle ranges,as the expansion angle increases,the distance between two kidney vortex centers becomes larger and the height of kidney vortex center decreases successively.The average cooling efficiency of spanwise would increase about15% between neighboring two angles in M=0.5,and the cooling efficiency of β =20° is greatly improved than other structures in M=1.5;γ =10° is the best in backward angle ranges,as the backward angle becomes larger,the structure coupling would be larger.It leads the extension of internal structure becomes larger which strengthens the Coanda effect inside the hole.In that way,the upward momentum of outlet would greatly reduce and the covering ability of air film near the center line would greatly improve,but the lateral covering ability of air film would badly reduce. |
